1. Field of the Invention
The invention relates to perforated glass plates as well as to a method and apparatus for producing such plates and somewhat more particularly the invention relates to glass plates having fine sized perforations therein so as to be useful in gas display discharge devices, such as plasma display devices, particularly in such devices which have a high picture point density.
2. Prior Art
German Offenlegungsscrift No. 2,412,869 (which corresponds to U.S. Pat. No. 3,956,667 and which is incorporated herein by reference) describes a luminescent gas discharge display device. In order to produce a plasma display with this type of device, a so-called control plate is necessary for controlling the individual picture points. This control plate divides the interior space of such display devices into two realms, a plasma realm and a post-acceleration realm. Generally, the control plate comprises a perforated glass plate having a matrix-type array of metal tracks or conductor paths surrounding such perforations. In such a matrix array, electrodes or conductor path facing the plasma realm extend horizontally (line or row tracks) while the electrodes facing the post-acceleration realm extend vertically (column tracks). With such an electrode arrangement, each picture point in the display device can be individually controlled. In this manner, electrons present in the plasma realm can be controllable moved via a circuit through the perforated glass plate in the post-accelaration realm and onto the luminescent screen.
The number of perforations or holes in glass plate of the above-described type is determined by a given utility and, in plasma display devices, is determined by the number of picture points desired. For example, with present-day television line scanning patterns on a picture tube having a diagonal dimension of 67 cm, the control array comprises a horizontal grid of 0.32 mm and a vertical grid of 0.64 mm and determines the number of holes in a control plate. Since such holes or perforations must be provided by etching, control limitation in the manufacture of plates containing such holes results, since a specific relationship between the thickness of a glass plate, the hole size and the spacing of the holes must be accurately attained. In addition, since etching occurs after the desired conductor paths or tracks have been positioned on the plate surfaces, a danger exists that such tracks will either insufficiently adhere to the glass surfaces or be completely separated therefrom during the etching process because of the undercutting or underetching (lateral etching) of the glass area beneath the tracks. Accordingly, control problems exists in etching plates having predetermined geometric patterns and a solution is required which allows such etching and satisfies all of the required conditions.